The present invention relates to apparatus and methods for authenticating items such as documents, cards, currency or other objects using difficult-to-forge markings on the items.
The prior art uses many different difficult-to-forge markings on items to thwart counterfeiting, forgery, frauds, identity theft, security violations. Marked items include documents such as bank documents and legal papers, cards such as credit cards and identification cards, currency, works of art, memorabilia and other valuable items. Some marking techniques use substances such as ink which contains an unique material not apparent to visual observation but can be detected by a special process or equipment.
One unique material used in marking items includes DNA (deoxyribonucleic acid) fragments derived from human, animal or plant sources. The DNA can be identified by processes similar to those used to identify a perpetrator from DNA found at a crime scene or used to identify a genetic disease of a patient. Such processes usually include extraction of the DNA and amplification by polymerase chain reaction. The amplified DNA is detected using electrophoresis, attachment of a radioactive or fluorescent marker, and/or reaction within cells of a microchip. These processes are performed in a laboratory and generally require long time periods as well as destruction of at least a portion of the marking material.
Spectrometry such a Raman spectrometry can be employed to rapidly identify certain materials which have a relatively high Raman response and low fluorescence. DNA is characterized by a relatively low Raman response and high fluorescence and thus is generally considered unsuited for identification by Raman spectrometry. Surface enhanced Raman spectrometry (SERS) wherein a roughened metal surface or metal colloid increases the Raman response is employed to identify certain abnormal DNA associated with disease.